2,592 research outputs found
Single-photon emitting diode in silicon carbide
Electrically driven single-photon emitting devices have immediate
applications in quantum cryptography, quantum computation and single-photon
metrology. Mature device fabrication protocols and the recent observations of
single defect systems with quantum functionalities make silicon carbide (SiC)
an ideal material to build such devices. Here, we demonstrate the fabrication
of bright single photon emitting diodes. The electrically driven emitters
display fully polarized output, superior photon statistics (with a count rate
of 300 kHz), and stability in both continuous and pulsed modes, all at room
temperature. The atomic origin of the single photon source is proposed. These
results provide a foundation for the large scale integration of single photon
sources into a broad range of applications, such as quantum cryptography or
linear optics quantum computing.Comment: Main: 10 pages, 6 figures. Supplementary Information: 6 pages, 6
figure
New results on heavy hadron spectroscopy with NRQCD
We present results for the spectrum of b-bbar bound states in the quenched
approximation for three different values of the lattice spacing. Results for
spin-independent splittings are shown to have good scaling behaviour;
spin-dependent splittings are more sensitive to discretisation effects. We
discuss what needs to be done to match the experimental spectrum.Comment: 3 pages, contribution to Lattice'9
High superconducting anisotropy and weak vortex pinning in Co doped LaFeAsO
Here, we present an electrical transport study in single crystals of
LaFeCoAsO ( K) under high magnetic fields. In
contrast to most of the previously reported Fe based superconductors, and
despite its relatively low , LaFeCoAsO shows a superconducting
anisotropy which is comparable to those seen for instance in the cuprates or
, where
is the effective mass anisotropy. Although, in the present case and as in all
Fe based superconductors, as . Under
the application of an external field, we also observe a remarkable broadening
of the superconducting transition particularly for fields applied along the
inter-planar direction. Both observations indicate that the low dimensionality
of LaFeCoAsO is likely to lead to a more complex vortex
phase-diagram when compared to the other Fe arsenides and consequently, to a
pronounced dissipation associated with the movement of vortices in a possible
vortex liquid phase. When compared to, for instance, F-doped compounds
pertaining to same family, we obtain rather small activation energies for the
motion of vortices. This suggests that the disorder introduced by doping
LaFeAsO with F is more effective in pinning the vortices than alloying it with
Co.Comment: 7 figures, 7 pages, Phys. Rev. B (in press
Low temperature heat capacity of Fe_{1-x}Ga_{x} alloys with large magneostriction
The low temperature heat capacity C_{p} of Fe_{1-x}Ga_{x} alloys with large
magnetostriction has been investigated. The data were analyzed in the standard
way using electron () and phonon () contributions. The
Debye temperature decreases approximately linearly with increasing
Ga concentration, consistent with previous resonant ultrasound measurements and
measured phonon dispersion curves. Calculations of from lattice
dynamical models and from measured elastic constants C_{11}, C_{12} and C_{44}
are in agreement with the measured data. The linear coefficient of electronic
specific heat remains relatively constant as the Ga concentration
increases, despite the fact that the magnetoelastic coupling increases. Band
structure calculations show that this is due to the compensation of majority
and minority spin states at the Fermi level.Comment: 14 pages, 6 figure
Phase transitions and iron-ordered moment form factor in LaFeAsO
Elastic neutron scattering studies of an optimized LaFeAsO single crystal
reveal that upon cooling, an onset of the tetragonal (T)-to-orthorhombic (O)
structural transition occurs at K, and it exhibits a
sharp transition at K. We argue that in the
temperature range to , T and O structures may
dynamically coexist possibly due to nematic spin correlations recently proposed
for the iron pnictides, and we attribute to the formation of
long-range O domains from the finite local precursors. The antiferromagnetic
structure emerges at K, with the iron moment
direction along the O \emph{a} axis. We extract the iron magnetic form factor
and use the tabulated of Fe, Fe and Fe to
obtain a magnetic moment size of 0.8 at 9.5 K.Comment: 7 pages, 6 figures, 3 table
High-fidelity adiabatic inversion of a electron spin qubit in natural silicon
The main limitation to the high-fidelity quantum control of spins in
semiconductors is the presence of strongly fluctuating fields arising from the
nuclear spin bath of the host material. We demonstrate here a substantial
improvement in single-qubit gate fidelities for an electron spin qubit bound to
a P atom in natural silicon, by applying adiabatic inversion instead of
narrow-band pulses. We achieve an inversion fidelity of 97%, and we observe
signatures in the spin resonance spectra and the spin coherence time that are
consistent with the presence of an additional exchange-coupled donor. This work
highlights the effectiveness of adiabatic inversion techniques for spin control
in fluctuating environments.Comment: 4 pages, 2 figure
Magnetic and structural transitions in LaNaFeAs single crystals
LaNaFeAs single crystals have been grown out of an
NaAs flux in an alumina crucible and characterized by measuring magnetic
susceptibility, electrical resistivity, specific heat, as well as single
crystal x-ray and neutron diffraction. LaNaFeAs single
crystals show a structural phase transition from a high temperature tetragonal
phase to a low-temperature orthorhombic phase at T\,=\,125\,K. This
structural transition is accompanied by an anomaly in the temperature
dependence of electrical resistivity, anisotropic magnetic susceptibility, and
specific heat. Concomitant with the structural phase transition, the Fe moments
order along the \emph{a} direction with an ordered moment of
0.7(1)\, at \emph{T}\,=\,5 K. The low temperature stripe
antiferromagnetic structure is the same as that in other
\emph{A}FeAs (\emph{A}\,=\,Ca, Sr, Ba) compounds.
LaNaFeAs provides a new material platform for the
study of iron-based superconductors where the electron-hole asymmetry could be
studied by simply varying La/Na ratio.Comment: 9 pages, 7 figures, to appear in Physical Review
- …